To identify the quality of the thermos bottle, take the bladder out of the bottle shell to see if the glass tail tube (shaped like a teat) under the bottle is damaged. If it is broken, it means that the air has entered the middle of the two layers of glass and it is impossible to keep the heat preservation. If it is not broken, check the silver film of the inner and outer bottles. If the silver film is black or peeled off, it will also affect the heat preservation performance.
Some people like to listen with their ears when buying a thermos bottle. They think that hearing the "buzzing" sound is to keep warm. In fact, this method is not scientific, because the so-called "buzzing" sound is caused by resonance, which means that The shape of the air column can resonate with the sound of the same frequency, making the sound louder. When the frequency of a certain sound around us is the same as the natural frequency of the air column in the gallbladder, it will resonate and make a "buzzing" sound. At the same time, if there is a small crack in the lining of the bottle or the outer glass is broken, there may still be a "buzzing" sound. Therefore, when choosing a thermos bottle, you cannot use the "buzzing" sound as a sign of whether it is warm or not.
The outer surface of the metal shell should be free of irregularities, nicks, cracks, sand holes, bumps and other defects. The bottom of the shell should have small holes, the paint layer should be uniform and firm, the color should be bright, and there should be no leakage or paint removal. The mouth of the bottle bladder should be perfectly round, and there should be no gaps, too thin, too thick, uneven thickness, roughness, skewed and deformed phenomena. The bottle body should be round, and there should be no unevenness. The bottom is a smooth semicircle with no significant deviation. The tail of the bottle is not too long, and the silver surface is bright and clean, silvery white. Observing the interior under the lamp should not transmit light. It is not suitable to buy when the following problems occur; there are small cracks on the surface of the glass (mostly at the bottom of the bottle); the crooked mouth prevents the bottle stopper from being tightly closed and affects the insulation performance.